1. Field of the Invention
This invention relates to expandable polylactic acid resin particles, to expanded polylactic acid resin beads and to a molded article obtained from the expanded polylactic acid resin beads. More specifically, the present invention is directed to a polylactic acid resin in-mold foam molding having good appearance and excellent fusion bonding between expanded beads, to expanded polylactic acid resin beads suitable for producing such a foam molding, and to expandable polylactic acid resin particles suitable for producing such expanded beads.
2. Description of Prior Art
Foamed bodies of generally employed resins such as polyethylene, polypropylene and polystyrene resins are now used in various fields because of their good heat insulating properties, cushioning properties and lightness in weight. Because of accelerated depletion of petroleum resources from which the generally employed resins are made, however, much attention is now being paid upon polylactic acid resins derived from plants such as corn. Polylactic acid resins are promising because they are decomposable, when left in the environment, into carbon dioxide and water by biological degradation. In particular, environmentally friendly foamed bodies of a polylactic acid resin such as in-mold foam moldings of expanded polylactic acid resin beads are now being developed.
For example, Japanese Unexamined Patent Publication No. JP-A-2002-20525 proposes expanded polylactic acid resin beads useful for producing in-mold foam moldings. With the expanded beads, however, steam having a temperature of 141 to 161° C. must be used to produce a molding in a mold because of high degree of crystallization of the resin. Therefore, it is necessary to use a specific molding apparatus which can withstand the high pressure steam. Further, a large amount of steam should be consumed. Additionally, part of the polylactic acid resin which has not yet been crystallized is susceptible to be thermally decomposed during the molding step, thereby to cause shrinkage and surface undulations of the resulting foam molding.